code: def test_dissolve_none_mean(nybb_polydf):
      test = nybb_polydf.dissolve(aggfunc="mean", numeric_only=True)
      expected = GeoDataFrame(
          {
              nybb_polydf.geometry.name: [
                  nybb_polydf.geometry.union_all()
              ],
              "BoroCode": [3.0],
              "manhattan_bronx": [5.4],
          },
          geometry=nybb_polydf.geometry.name,
          crs=nybb_polydf.crs,
      )
      assert_frame_equal(expected, test, check_column_type=False)
  
imports: import warnings
  import numpy
  import pandas
  import geopandas
  from geopandas import GeoDataFrame, read_file
  from pandas.testing import assert_frame_equal
  import pytest
  from geopandas._compat import PANDAS_GE_15, PANDAS_GE_20
  from geopandas.testing import assert_geodataframe_equal, geom_almost_equals
label_desc: Use image node_id 15 for calling a global function with example usage: test_dissolve_none_mean(nybb_polydf) without return types